1. Field of the Invention
The present invention relates to a producing method of a mask in which an original or master plate to be transferred onto a substrate such as a wafer in a lithography process for producing semiconductor devices, image pickup devices (CCDs etc.), liquid crystal displays, plasma displays, thin film magnetic heads and the like. The present invention also relates to an exposure method and an exposure apparatus used for this producing method. For example, the invention is suitably used for producing a mask and the like such as a transparent reticle using excimer laser as exposure beam, a reflective reticle using EUV light such as soft X-ray as the exposure light, and a membrane structure using electron beam as the exposure beam.
2. Description of the Related Art
Conventionally, when a semiconductor device is produced, in order to transfer a pattern of a reticle (or photo-mask) as a mask onto each shot region of a wafer on which a photoresist is applied, an i line (wavelength 365 nm) of a mercury lamp as exposure beam, or KrF excimer laser (wavelength 248 nm) is used, and a projection exposure apparatus (stepper or the like) using a projection optical system having the number of openings NA of about 0.7 is used. If a wavelength of the exposure beam is defined as xcex and a predetermined process coefficient is defined as k, resolution on a wafer is expressed as kxc3x97xcex/NA. Therefore, a conventional minimum line width of an image of a line and space pattern that can be transferred onto the wafer is about 180 nm. The size of the conventional reticle is usually 5xc3x975 inches or 6xc3x976.
In this case, since a projection magnification of a projection optical system is about xc2xc or ⅕, a line width of a pattern of a reticle corresponding to the minimum line width (when the projection magnification is xc2xc) is about 720 nm. A conventional reticle having such a pattern is produced by directly forming the original pattern on a predetermined substrate using an electron beam drawing apparatus.
As described above, the conventional reticle is produced by directly forming, onto a substrate of about 6xc3x976 inches at the maximum, an original pattern whose a minimum line width becomes about 180 nm on a wafer. However, since the electron beam drawing apparatus continuously forms various portions of the original pattern with beams of a predetermined cross sectional shape, there is inconvenience that the pattern-forming time becomes long and the producing time of reticle becomes long. Especially, since the same reticles are usually used as working reticles concurrently by a plurality of producing lines, it is necessary to produce a plurality of reticles having the same original pattern. At that time, the pattern of each of the working reticles is formed by the electron beam drawing apparatus, time required for producing the reticles becomes extremely long.
Further, precision of about 5% of the minimum line width in an entire surface of the reticle is required as pattern-forming precision. Therefore, if the minimum line width is 720 nm, precision of about 36 nm is required. Thus, when the size of the reticle is 6xc3x976 inches, precision of about 36 nm (≈2.4xc3x9710xe2x88x927) is required for length of about 150 mm. Such precision is almost limit of the current electron beam drawing apparatus when drift of electron beam is taken into consideration.
Further, the resolution will further be improved so as to meet the increased packing density of the semiconductor device and the like. That is, for future several years, in order to transfer a pattern having the minimum line width of about 180 to 100 nm onto a wafer, ArF excimer laser light (wavelength is 193 nm), F2 laser light (wavelength is 157 nm) and laser light of vacuum ultraviolet (VUV) such as solid laser and the like are under review. As a reticle for exposure beam of the vacuum ultraviolet longer than about 100 nm, a transparent reticle using fluorite (CaF2) as a substrate can be used.
In order to further enhance the resolution for the next generation semiconductor device, an exposure apparatus in which extreme ultraviolet light (EUV light) such as soft X-ray (wavelength is about 13 to 6 nm) is used as exposure beam, and reflection system of reduced magnification using a combination of about three to five concave mirrors and convex mirrors is used as the projection optical system is under development. When the EUV light is used, since there is not optical material having excellent transmittance, it is considered that a reticle to be used is a transparent reticle.
The use of an electron beam exposure apparatus in which a mask (stencil mask or the like) of a membrane structure having predetermined opening patterns in thin film members formed on a wafer into a lattice shape is irradiated with electron beam, an image of the opening pattern in the film member is transferred onto a substrate to be exposed while stitching screens at reduced magnification, thereby transferring a pattern of large area at high resolution is also under review. It is expected that resolution of about 130 to 30 nm can be obtained using the exposure apparatus or the electron beam exposure apparatus using the EUV light.
In order to obtain resolution of about 180 to 30 nm on a wafer, if the projection magnification of the projection optical system is xc2xc, the minimum line width of the reticle pattern is about 720 to 120 nm. It is expected that the size of the future reticle will be about 9xc3x979 inches. Therefore, if the pattern-forming precision is about 5% of the minimum line width, precision required for the electron beam drawing apparatus is about 36 to 6 nm (about 1.6xc3x9710xe2x88x927 to 2.6xc3x9710xe2x88x928) with respect to a length of about 230 nm, but it is difficult under present circumstances to realize such a high precision. Further, if the area of the reticle becomes greater and the pattern becomes finer, the pattern-forming time becomes longer. Therefore, especially when a plurality of working reticles are produced, there is inconvenience that the producing time becomes excessively long.
In recent years, attention is directed toward technique for disposing previously designed various circuit units such as CPU or memory into a predetermined arrangement, these units are connected to one another through wires, thereby producing a semiconductor device that can achieve a desired function as in a case in which ASIC (application-specific IC) is produced. According to this technique, it is possible to develop semiconductor devices having various functions in a short time and thus, it is expected that the technique will widely be utilized in fields of multimedia, digital TV and the like. However, in such a case also, if the original pattern of each reticle is formed using the electron beam drawing apparatus, since the producing time of the reticle becomes long, there is inconvenience that developing time can not be shortened so much especially when various semiconductor devices are developed.
Thereupon, recently, a method in which an original pattern having an enlarged pattern on a reticle is prepared, this original pattern is divided into a plurality of parent patterns, they are formed on master reticles, images of the patterns of the plurality of master reticles are transferred onto a glass substrate while stitching screens using reduction projection type exposure apparatus, thereby producing reticles (working reticles) for actually light exposure is under review. When the image is transferred while stitching screens in this manner, it is necessary to reduce stitching error of a boundary portion (stitching portion) of adjacent parent patterns, and to reduce variation in exposure light amount in the vicinity of the boundary portion.
As an exposure method that can be used to reduce the stitching error and to reduce variation in exposure light amount, there is a method as disclosed in Japanese Patent Application Laid-open No. 6-132195 and corresponding U.S. Pat. No. 5,477,304 in which in order to transfer an image of a reticle pattern in each shot region on a wafer while stitching the screens, illumination distribution of illumination region of the exposure light is formed into a trapezoidal shape in which opposite ends are gradually lowered, and image of adjacent reticle patterns are overlapped on a boundary portion of a predetermined width. As a first method for forming the illumination distribution of the illumination region into the trapezoidal shape, there is a method in which a disposing surface of a reticle blind (variable field aperture) for defining the illumination region is defocus on the illumination region (pattern surface of reticle). According to this method, however, when shape of the opening aperture of an illumination optical system is switched from a circle (normal illumination) to a plurality of decentered opening (deformed illumination), there is an adverse possibility that the shape of the illumination distribution is not trapezoidal shape.
In order to prevent the shape of the illumination distribution from being deformed, the defocus amount of the reticle blind may be varied in accordance with illumination condition for example, but there is inconvenience that the mechanism of the illumination optical system is complicated.
Further, in order to form the illumination distribution of the illumination region into substantially the trapezoidal shape, there is proposed a method for moving a blade constituting the reticle blind into exposure light. However, there is inconvenience that this method also complicates a driving mechanism of the reticle blind and the mechanism of the illumination optical system is complicated.
There is considered a method for forming the illumination distribution of the illumination region into the trapezoidal shape by making ends of the reticle blind disposed in conjugate position with the illumination region semi-transparent. According to this method, however, if a foreign substance is attached to the semi-transparent portion, uneven illumination is generated in the illumination region. In order to avoid this, it is necessary to enhance the precision of a dustproof mechanism for gas supplied to the illumination optical system. Therefore, there is inconvenience that the mechanism of the illumination optical system is complicated.
In view of the above circumstances, it is a first object of the present invention to provide a producing method of a mask capable of producing a mask on which a transfer pattern is formed in a short time with high precision.
It is a second object of the invention to provide a producing method capable of producing, in a short time, a mask having a pattern which can be formed by disposing various circuit units according to a predetermined positional relation and by connecting the units through wire patterns or the like.
It is a third object of the invention to provide a producing method of a mask on which a fine transfer pattern of a large area is formed in a short time with high precision.
It is a fourth object of the invention to provide a projection exposure method in which when a transfer pattern is divided into a plurality of patterns and images of the patterns are transferred while stitching screens, a mechanism of an illumination optical system is not complicated, stitching error of boundary portions of images between a plurality of patterns is reduced, and uneven exposure light amount in the vicinity of the boundary portion can be reduced.
It is a fifth object of the invention to provide a projection exposure method when one mask pattern is produced while stitching screens, stitching error of images of a plurality of patterns and the mask pattern can be produced with high precision.
It is another object to provide a projection exposure apparatus capable of carrying out the above projection exposure method, and a producing method of a device using the projection exposure method.
According to a first aspect of the present invention, there is provided a producing method of a mask formed with a transfer pattern and to be irradiated with a predetermined exposure beam, comprising:
making design data of an original pattern obtained by enlarging the transfer pattern, applying photosensitive material into which a coloring matter which absorbs light in a predetermined wavelength region is mixed onto at least one first substrate, and forming at least a portion of the original pattern on the first substrate,
developing the photosensitive material on the at least one first substrate, and
with the at least one first substrate being used as a parent mask having a mask pattern made of the photosensitive material remained after developing the photosensitive material, exposing a reduced image of the pattern of the parent mask onto a second substrate while stitching the reduced image using a projection exposure apparatus which carries out reduction projection using illumination light in a wavelength region absorbed by the photosensitive material.
According to the mask producing method of the first aspect of the present invention, the original pattern obtained by enlarging the transfer pattern is formed on the first substrate by an electron beam drawing apparatus for example. Then, using photosensitive material left by development of the photosensitive material on the first substrate is used as the mask pattern, and the mask pattern is reduction projected using the exposure apparatus using light having wavelength region absorbed by coloring matter in the photosensitive material as exposure light. With this method, the mask can be produced at high speed without carrying out a step such as deposition of chromium film and etching with respect to the first substrate. This electron beam drawing apparatus may form the enlarged pattern of the transfer pattern. Thus, if the enlargement magnification is set to xcex1, an influence of the pattern-forming error is reduced to about 1/xcex1 and thus, the transfer pattern is formed with high precision.
According to a second aspect of the present invention, there is provided a producing method of a mask formed with a transfer pattern, comprising
dividing the transfer pattern into an existing pattern portion and a newly-forming pattern portion based on design data of the transfer pattern,
forming an original pattern corresponding to a pattern of the newly-forming pattern portion onto a first substrate to prepare a first parent mask, and
with a mask formed with another original pattern corresponding to a pattern of the existing pattern portion being used as a second parent mask, exposing images of patterns of the first and second parent masks onto a second substrate which is to become the mask while stitching the images.
According to the mask producing method of the second aspect of the present invention, only the original pattern corresponding to the newly-forming pattern is newly formed by the electron beam drawing apparatus for example, and an already-formed parent mask is commonly used for the second parent mask on which the original pattern corresponding to the existing pattern is formed. In this case, since the newly-forming pattern is a portion of the entire transfer pattern, if the ratio of the pattern-forming error with respect to the entire length of the pattern to be formed is judged as being substantially constant, the pattern-forming error of the newly-forming pattern can be reduced as compared with a case in which the entire original pattern is formed. Therefore, as compared with a case in which the entire original pattern is formed by the electron beam drawing apparatus, it is possible to form the mask in a short time and with high precision.
According to a third aspect of the present invention, there is provided a producing method of a mask formed with a transfer pattern including a predetermined linear pattern, comprising:
diving an enlarged pattern of the transfer pattern into a plurality of parent patterns from a position corresponding to an intermediate portion of the linear pattern as a boundary portion, and
projecting and exposing reduced images of the plurality of parent patterns onto a substrate which is to become the mask while stitching the reduced images, wherein,
portions of the plurality of parent patterns corresponding to the boundary portion of the linear pattern are provided with overlapped portions each having a predetermined width in its longitudinal direction, and the overlapped portions are respectively provided with tapered portions each having a wide tip end.
According to the mask producing method of the third aspect of the present invention, the enlarged pattern is divided into a plurality of parent patterns, and the images of the parent patterns are transferred while stitching the screens. With this method, the transfer pattern having large area can be formed in a short time. If a design length of the overlapping portion of the reduced images of the plurality of parent patterns is defined as 2xc3x97xcex94L, and if the reduced images are stitched and exposed, a boundary portion having a length of 2xc3x97xcex94L and a thick central portion is formed in a state in which there is no positional deviation under normal exposure light amount. However, the overlapping portion is exposed twice and is also exposed to light that wraps around. This boundary portion can be made substantially flatly by increasing the exposure light amount (over exposure). At that time, even if the positioning error of about xc2x1xcex94L of the reduced images of the parent patterns is generated in the longitudinal direction and in a direction intersecting with the longitudinal direction, the boundary portion does not become thin. Therefore, a fine pattern can be formed with high precision.
According to a fourth aspect of the present invention, there is provided a projection exposure method, comprising:
diving a predetermined pattern into a plurality of mask patterns, and exposing images of the plurality of mask patterns onto a substrate while stitching screens through a projection optical system, thereby transferring an entire image of the predetermined pattern onto the substrate, wherein
when the predetermined pattern is divided into the plurality of mask patterns, boundary portions of adjacent two mask patterns are respectively provided with overlapping portions of superposed portions,
when an image of each mask pattern of the plurality mask patterns is exposed onto the substrate through the projection optical system,
the mask pattern and the substrate are moved in synchronously with a predetermined visual field of the projection optical system such that the pattern of the mask pattern other than the overlapping portion does not come out from the predetermined visual field and a pattern of the overlapping potion goes out from the visual field.
According to the projection exposure method of the fourth aspect of the present invention, by exposing the image while stitching the screens using a static exposure type (full field exposure type) projection exposure apparatus, the image of one pattern is transferred onto the substrate. That is, as shown in FIG. 17A1, a substrate 218 is positioned such that most part of partial overlapping portions 237A and 240A in a mask pattern with respect to a visual field is within a visual field 210, and remaining overlapping portions 238A and 239A are out of the visual field 210. After the substrate 218 is positioned such that overlapping error is within a tolerance, the visual field 210 is irradiated with exposure beam with uniform illumination distribution.
Thereafter, the mask pattern is moved in a direction shown with an arrow 243R with respect to the visual field 210, and when the remaining overlapping portions 238A and 239A come within the visual field 210 completely as shown in FIGS. 17B1 and 17C1, the irradiation of the exposure beam is stopped. With this operation, the distribution of the exposing amount on the corresponding substrate 218 is formed into a trapezoidal shape as shown with a folded line 244A in FIG. 18A for example. That is, a trapezoidal illumination distribution can be obtained without complicating the mechanism of the illumination optical system, and uneven exposure light amount in the vicinity of the boundary portion obtained by overlapping the adjacent mask pattern images is reduced.
Further, as shown in FIGS. 17A2, 17B2 and 17C2, if the substrate 218 is moved with respect to an exposure region 230 that is conjugate with the visual field 210 in synchronism with movement of each mask pattern, the stitching error in the boundary portion of the adjacent mask pattern images is reduced by effect of average.
According to a fifth aspect of the present invention, there is provided a projection exposure method, comprising:
diving a predetermined pattern into a plurality of mask patterns, and exposing images of the plurality of mask patterns onto a substrate while stitching screens through a projection optical system, thereby transferring an entire image of the predetermined pattern onto the substrate, wherein
the predetermined pattern is divided into the plurality of mask patterns along at least a predetermined direction, boundary portions of adjacent two mask patterns in the predetermined direction are provided with overlapping portions of superposed portions,
when an image of each mask pattern of the plurality of mask patterns is exposed onto the substrate through the projection optical system,
in a state in which an image of a pattern, of the mask pattern, in a visual field which is fixed to the projection optical system and is elongated in the predetermined direction is exposed onto the substrate through the projection optical system, the mask pattern and the substrate are scanned in synchronously with each other at the same speed ratio as a projection magnification of the projection optical system in a direction intersecting substantially at right angles with the predetermined direction with respect to the visual field, and
the mask pattern and the substrate are moved in synchronously with each other in the predetermined direction in accordance with exposure time and a width of the overlapping portion of the mask pattern with respect to the visual field.
According to the projection exposure method of the fifth aspect of the present invention, one pattern image is transferred onto the substrate 259 by exposing the image using a scanning type projection exposure apparatus such as a step and scan type while stitching screens. At that time, as shown in FIG. 19 for example, widths (in a predetermined direction) of opposite side overlapping portions 253, 254 of a mask pattern 255 to be exposed and a portion 252 except these portions 253, 254 are defined as L1 and L1, and a width of the visual field 210 on the mask pattern in the predetermined direction is defined as L2, the width L2 is set as follows:
L2=11+2xc3x97Lxe2x80x83xe2x80x83(1)
In order to make the illumination distribution with respect to the overlapping portion such that the illumination distribution as a whole becomes smaller as approaching the end thereof, if a width in a scanning direction intersecting with the predetermined direction (direction to be scanned) of the visual field is defined as H and scanning speed of the mask pattern with respect to the visual field is defined as VR, it is desirable that the mask pattern is vibrated (moved) with amplitude L with respect to the direction to be scanned and with cycle TR satisfying the following conditions using one or more integers n as one example:
VRxc3x97TR=H/nxe2x80x83xe2x80x83(2)
i.e.,
TR=H/(nxc3x97VR)xe2x80x83xe2x80x83(3)
This means that when the mask pattern is moved through the width H of the visual field in the scanning direction, the mask pattern is vibrated n-times in the direction to be scanned as shown in FIGS. 19A to 19E. With this, the mask pattern is moved along a sinusoidal wave with respect to the visual field, the distribution of the exposure light amount on the substrate after the scanning exposure is formed into the trapezoidal shape as shown with a curved line 258A in FIG. 20 for example, and the uneven exposure light amount in the vicinity of the boundary portion obtained by overlapping the images of the adjacent mask patterns becomes small.
Further, if the substrate 259 is moved along a sinusoidal wave with respect to an exposure region 230S that is conjugate with the visual field 210S in synchronism with movement of each mask pattern along a sinusoidal wave as shown in FIG. 19F for example, the stitching error in the boundary portion of the adjacent mask pattern images is reduced by effect of average.
Furthermore, in the projection exposure methods of the fourth aspect and fifth aspect of the present invention, if a predetermined pattern to be transferred onto the substrate is one mask pattern, stitching error when the mask pattern is exposed to light by screen stitching method is reduced.
According to a sixth aspect of the present invention, there is provided a projection exposure apparatus which exposes a pattern formed on a mask onto a substrate through a projection optical system, the projection optical system being an optical system which exposes an image of a pattern of the mask within a predetermined visual field onto the substrate, comprising:
a mask stage capable of holding the mask and moving in a predetermined direction,
a substrate stage capable of holding the substrate and moving two-dimensionally including the predetermined direction, and
a control system which drives the mask stage and the substrate stage to move the mask and the substrate in synchronous with each other in the predetermined direction such that, when an entire image of the pattern of the mask is exposed onto the substrate through the projection optical system, a portion of the pattern of the mask does not come out from the visual field and a pattern other than the portion goes out from the visual field.
According to the projection exposure apparatus of the sixth aspect of the present invention, the projection exposure method of the fourth aspect of the present invention can be carried out.
According to a seventh aspect of the present invention, there is provided a projection exposure apparatus which exposes a pattern formed on a mask onto a substrate through a projection optical system, the projection optical system being an optical system which exposes an image of the pattern of the mask in a visual field which is longer in a predetermined direction, comprising:
a mask stage capable of holding the mask and moving in the predetermined direction and in a direction intersecting substantially at right angles with the predetermined direction,
a substrate stage capable of holding the substrate and moving in a two-dimensional directions including the predetermined direction, and
a control system which, when an image of a pattern of the mask in the visual field is exposed onto the substrate through the projection optical system, drives the mask stage and the substrate stage to move the mask stage and the substrate stage in synchronous with each other in a direction intersecting the predetermined direction substantially at right angles and to move the mask and the substrate in the predetermined direction in synchronous with each other such that an end of the pattern of the mask goes out from the visual field by a predetermined width.
According to the projection exposure apparatus of the seventh aspect of the present invention, the projection exposure method of the fifth aspect of the present invention can be carried out.
According to a eighth aspect of the present invention, there is provided a producing method of a device comprising a step for transferring a device pattern (including a mask pattern, a pattern for a semiconductor device, etc.) onto a work piece using a projection exposure method as recited in claim 4.
According to a ninth aspect of the present invention, there is provided a projection exposure method, comprising the step of transferring a mask pattern is transferred to a plurality block regions arranged in a first direction on a substrate through a projection optical system to form a predetermined pattern on the substrate, peripheral portions of the block regions being partially overlapped, wherein
in order to transfer the mask pattern to one block region of the plurality of block regions, the mask pattern and the substrate are moved in synchronous with each other with respect to a predetermined region where energy beam is irradiated within a visual field of the projection optical system, and moving directions of the mask pattern and the substrate are set to a direction which is intersecting with the first direction and with a second direction which intersects with the first direction at right angles such that an irradiating amount of the energy beam is gradually reduced at the peripheral portion in the one block region with respect to the first direction.